CH: 14

Why do your ears sometimes pop when you change altitude—say, moving in a skyscraper elevator or descending in an airplane?

-A change in altitude means a change in air pressure, this causes a temporary imbalance in the pressures on the two sides of your eardrum.

How does the mass of the air in your bedroom compare to your mass? The mass of the air is zero. The mass of the air is much less than your mass. The mass of the air is much greater than your mass. They are approximately equal.

-They are approximately equal

Atmospheric pressure decreases with increasing _________ -speed of molecules in the air. -amounts of sunshine -temperature -altitude

-altitude :A change in altitude means a change in air pressure. :The exact height of the atmosphere has no real meaning because the air gets progressively thinner and thinner the higher one travels upward. :The atmosphere. Air is more com- pressed at sea level than at higher altitudes. Like feathers in a huge pile, what's at the bottom is more squashed than what's nearer the top.

A column of mercury 76 cm tall has a weight that is equal to ___________. -that of a column of water 10.3 m tall -normal atmospheric pressure -the weight of Earth's atmosphere -13.6 times the density of water

-that of column of water 10.3m tall :Could water be used to make a barometer? The answer is yes, but the glass tube would have to be much longer—13.6 times as long, to be exact. You may recognize this number as the density of mercury relative to that of water. A volume of water 13.6 times that of mercury is needed to provide the same weight as the mercury in the tube. So the tube would have to be at least 13.6 times taller than the mercury column. A water barometer would have to be 13.6 3 0.76 m, or 10.3 m high—too tall to be practical.

Atmospheric pressure is mainly due to the ___________. -average temperature of air -air pressure against Earth's surface -motion of air molecules -weight of air

-weight of air :Just as water pressure is caused by the weight of water, ATMOSPHERIC PRESSURE is caused by the weight of air. For Example: We have adapted so completely to the invisible air that we don't feel it, and we sometimes forget that it has weight. Perhaps a fish "forgets" about the weight of water in the same way. The reason we don't feel this weight crushing against our bodies is that the pressure inside our bodies balances the pressure of the surrounding air. There is no net force for us to sense.

How high would you have to go in the atmosphere for HALF (50%) of the mass of air to be below you? -18 km -30 km -11 km -5.6 km

5.6 km :50% of the atmosphere is below 5.6 km (99% of the atmosphere is below 30Km)

What is an ideal gas?

An ideal gas is one where the disturbing effects of forces between molecules and the finite size of molecules can be ignored.

About how many kilograms of air occupy a classroom that has a 200-m2 floor area and a 4-m-high ceiling? (Assume a chilly temperature of 10°C.)

At normal classroom temperature the mass of air is 1000 kg. The volume of air is area 3 height 5 200 m2 3 4 m 5 800 m3; each cubic meter of air has a mass of about 1.25 kg, so 800 m3 3 1.25 kg/m3 5 1000 kg.

What is the maximum height to which water can be sucked up through a straw?

At sea level, however strong your lungs may be, or whatever device you use to make a vacuum in the straw, the water cannot be pushed up by the atmosphere higher than 10.3 m.

Why doesn't the pressure of the atmosphere break windows?

Atmospheric pressure is exerted on both sides of a window, so no net force is exerted on the glass. If, for some reason, the pressure is reduced or increased on one side only, as when a tornado passes by, then watch out! Reduced outside air pressure created by a tornado can be disastrous.

A strong wind blows over the house shown in the figure. The wind is much stronger over the house's roof than lower down, and the house has an open chimney. A window on the ground floor is open, and so are the doors inside the house. Which way will air flow through the house?

In the window and out the chimney :A strong wind indicates fast speed and low pressure. SO that means that air pressure is lower at the chimney and higher outside the window, so air will flow in through the window and out through the chimney.

What happens when Dr. Hewitt takes the cans containing a small amount of hot water and dips them in cold water?

The cans get crushed

Why do the card and water do what they do when Dr. Hewitt flips them over?

The card is held up by atmospheric pressure that balances the weight of water

What happens when Dr. Hewitt places a card on a glass full of colored water and turns it upside down?

The card stays, and the water also stays in the glass.

A mountain-climber friend with a mass of 82 kg ponders the idea of attaching a helium-filled balloon to himself to effectively reduce his weight by 25% when he climbs. He wonders what the approximate size of such a balloon would be. Hearing of your physics skills, he asks you. Share with him your calculations that find the volume of the balloon.

Volume= 17 m3

Why do the cans containing a small amount of hot water do what they do in the experiment when Dr. Hewitt immerses them?

When the cans are suddenly cooled, the pressure inside them is less than the atmospheric pressure outside.

The weight of the atmosphere above 1 m2 of Earth's surface is about 100,000 N. Density, of course, becomes less with altitude. But suppose the density of air were a constant 1.2 kg/m3. Calculate where the top of the atmosphere would be. Express your answer to two significant figures and include the appropriate units.

h=8.5 km